The invention relates to a locking drive for a central locking system of a motor vehicle.
Electrically operated locking drives for central locking systems of motor vehicles must be able to move relatively smoothly so that the electric motors used can be of low power. Smoothness of movement does however entail the risk of force-transmitting parts of the locking drive being unintentionally moved, for example due to vibration or the like, resulting in an unintentional locking or unlocking of the system. It is known from German Patent application No. 28 47 588 for the push rod of a locking drive of a central locking system, driven by an electric motor, to be locked in its extreme positions by a spring catch. It is true that the spring catch enhances the inhibition in the extreme positions but it does, however, undesirably increase the resistance to displacement.
It is furthermore known to provide on the motor vehicle a plurality of locking positions, for example both on the doors and also on the trunk lid, via which all the locking drives of the central locking system can be centrally controlled. On the other hand, it is desirable to be able to open special locks, for example the trunk lock, even when the other locks have already been centrally locked. In the case of the central locking system according to German Patent application No. 28 47 588, there is connected in the drive path between key and trunk lock a spring which during opening is tensioned and which, after the key has been withdrawn from the lock, restores the locked condition. Similar springs which allow actuation of one lock regardless of the locked condition, for example by means of a "door button", are known from German Patent application No. 25 57 970. However, many of the conventional locking drives have the disadvantage that upon manual unlocking of one of the locking drives, the entire locking system is controlled to assume the unlocked condition. This is undesirable particularly when the trunk is being opened manually.
Finally, central securing systems are known which in addition to the locking drive have a second drive, for example a second electric motor, which moves a locking member into the path of displacement of the output rod of the locking drive so that the locked condition of the central locking system can also be maintained even under considerable externally acting forces.
The invention is directed towards provision of a simple locking drive for a central locking system, the force-transmitting parts of which offer only minimal resistance to displacement but which can however be reliably locked in their extreme positions.